Yes, unlike the a99, in which Sony obligingly managed to wring out more performance from ISO 50 and gets somewhat closer to RX1 level data points in spite of the SLT, the RX1 appears purely a metering workaround for the 'lower than DSLR' max s/speed.

The difference between these two cameras' sensor performance data is more apparent at high ISO, reflecting their likely 'use cases', so a trade-off most likely. D600 IQ also 'maxes out' at ISO 100. [All according to DxO.]